How you ever got that code to even compile with this line in it I don't get (quotes are missing and the semicolon should be a comma)

                               *[@att='type'] => \&changeTagAttrOrderH
+andler;
[download]

But anyway, your problem might be that this line

        $rootElt->set_atts( { $att1 => $att1Val, $att2 => $att2Val, $a
+tt3 => $att3Val});
[download]

As a simple standalone example, this code gives the attributes in a fixed order but it doesn't if you comment out the line with the arrow

use warnings; use strict;
use XML::Twig; use Tie::IxHash;
my $tw = XML::Twig->new("keep_atts_order", 1);
my %atts;
tie %atts, Tie::IxHash::; # <-----
%atts = ("year", 2010, "month", 3, "day", 5);
$tw->set_root(XML::Twig::Elt->new("date", \%atts));
$tw->flush; print "\n";
__END__
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Alternately use the set_att method like this:

use warnings; use strict;                                             
+                             
use XML::Twig;                                                        
+                      
my $tw = XML::Twig->new("keep_atts_order", 1);
$tw->set_root(my $de = XML::Twig::Elt->new("date"));
$de->set_att("year", 2010, "month", 3, "day", 5); 
$tw->flush; print "\n";
__END__
[download]

See below.

I made the code to run but it doesn't work :)

I mean that it doesn't do what it's suppose to do, this is the output:

after delete
            Attributes are: 
after new set
            Attributes are: day,month,year
<item>
...
    <ait:date-delivered month="02" day="09" year="2010"/>
...
</item>
[download]

It's funny but the order is different for all tree steps, in the original doc, aftet delete and insert an in the resulting doc.

'keep_atts_order' allows outputting the attributes in the same order as they were in the original document.

Does this mean XML::Twig it's not designed to work this way?

#!/usr/bin/perl
use strict;
use warnings;
use XML::Twig;

changeTagAttrOrder();

sub changeTagAttrOrder {
    my $t = XML::Twig->new(
        output_filter=>'safe',
        twig_handlers => {
            'ait:date-delivered' => \&changeTagAttrOrderHandler,
        },
        pretty_print => 'indented',
        keep_atts_order => 1,
    );
    $t->parse(\*DATA);
    $t->print;
    $t->purge;
}#end of changeTagAttrOrder

sub changeTagAttrOrderHandler {
    my( $t,$rootElt)= @_;
    my $curEltPath = $rootElt->path;

    my $att1Val = $rootElt->att('month');
    my $att2Val = $rootElt->att('year');
    my $att3Val = $rootElt->att('day');

    $rootElt->del_atts;
    print "after delete\n
            Attributes are: ".join(',',$rootElt->att_names())."\n";
    # $rootElt->set_atts(
    #     { month => $att1Val, year => $att2Val, day => $att3Val});
    $rootElt->set_att(day   => $att3Val);
    $rootElt->set_att(month => $att1Val);
    $rootElt->set_att(year  => $att2Val);

    print "after new set\n
            Attributes are: ".join(',',$rootElt->att_names())."\n";
}#end of changeTagAttrOrderHandler

__DATA__
<item>
<ait:process-info>
<ait:date-delivered year="2010" month="02" day="09"/>
<ait:date-sort year="2008" month="1" day="1"/>
<ait:status type="core" state="new" stage="S300"/>
</ait:process-info>
</item>
[download]

Regards, Stefan

The attribute order has no meaning in XML and I doubt there is a way to instruct XML::Twig to output them in a specific order.

You've fallen into a trap. Read the post again. It tries to use the keep_atts_order option of XML::Twig, and the whole purpose of that option is to be able to output the attributes in a particular order.